Prevalence of ultrasonographic gastrointestinal wall changes in dogs with acute pancreatitis: A retrospective study (2012‐2020)

Abstract Background Ultrasonographic gastrointestinal wall changes in dogs with acute pancreatitis (AP) are not well characterized in the literature. No detailed studies have described their prevalence, characteristics, distribution, or clinical relevance. Hypothesis/Objectives Describe the prevalence of ultrasonographic gastrointestinal wall changes in a population of dogs with AP and evaluate for associations between the presence of gastrointestinal wall changes and clinical or clinicopathological variables. Animals Referral population of 66 client‐owned dogs with AP. Methods Retrospective search of clinical records to identify dogs with AP. Clinical variables, clinicopathological variables and ultrasonographic findings were reported using descriptive statistics. A binary logistic regression model was used to evaluate for associations between the presence of gastrointestinal wall changes and clinical or clinicopathological variables. Results Sixty‐six dogs were included. Forty‐seven percent of dogs (95% confidence interval [CI], 35.0%‐59.0%; n = 31) with AP had ultrasonographic gastrointestinal wall changes. Gastrointestinal wall changes were most common in the duodenum and identified in 71% (n = 22) of affected dogs. Of dogs with gastrointestinal wall changes, 74.2% (n = 23) had wall thickening, 61.3% (n = 19) had abnormal wall layering, and 35.5% (n = 11) had wall corrugation. In the multivariable model, only heart rate remained an independent predictor of ultrasonographic gastrointestinal wall changes (P = .02). Conclusions and Clinical Importance Ultrasonographic gastrointestinal wall changes in this population of dogs with AP were common. Increased heart rate was the only independent predictor of gastrointestinal wall changes, which might imply more severe disease. Additional studies are required to elucidate whether ultrasonographic gastrointestinal wall changes reflect disease severity in AP.

severe disease. Additional studies are required to elucidate whether ultrasonographic gastrointestinal wall changes reflect disease severity in AP.

K E Y W O R D S
canine, gastroenterology, gastrointestinal ultrasound, hepatobiliary 1 | INTRODUCTION Acute pancreatitis (AP) is defined as acute, sterile and generally reversible pancreatic inflammation, characterized histologically by a neutrophilic infiltrate, edema, and necrosis. 1,2 Antemortem diagnosis typically relies upon a combination of history, physical examination findings, diagnostic imaging (generally ultrasonography or computed tomography), and clinicopathologic findings (hematology, serum biochemistry, and canine pancreatic lipase immunoreactivity). Histopathology is the gold standard for diagnosis of AP, but the morbidity associated with pancreatic biopsy and the heterogeneous distribution of pancreatic inflammation limit its use in practice. 2 Surrogate noninvasive tests, as described above, are more commonly utilized.
Ultrasonographic features of AP are well described in dogs. Pancreatic enlargement, hypoechoic or heterogeneous pancreatic parenchyma, hyperechoic peripancreatic mesentery, and peripancreatic free fluid are described in naturally-occurring [3][4][5][6][7][8] and experimentally-induced 9-11 pancreatitis. The sensitivity of ultrasound examination for the diagnosis of AP, based upon criteria of pancreatic hypoechogenicity with mesenteric hyperechogenicity, has been reported to be relatively poor at 68%. 12 A recent study stratifying cases by the presence of 1, 2, or 3 ultrasonographic criteria from pancreatic enlargement, altered pancreatic echogenicity or hyperechogenicity of the surrounding mesentery reported sensitivities of 89%, 72%, and 42% and specificities of 43%, 69%, and 92%, respectively. 3 Concurrent ultrasonographic gastrointestinal wall changes in dogs with AP are less widely reported in the literature. Gastric wall thickening, [13][14][15] increased small intestinal wall thickness, 11,15-17 small intestinal corrugation, 5,15 and blurred or apparent loss of gastrointestinal wall layering 13,14,16,17 have been reported. A recent case series reported gastric wall changes in 14 dogs with naturally-occurring AP, suspected to be reflective of gastric wall edema, but no prevalence data were reported. 14 The prevalence of gastrointestinal wall changes in naturally-occurring AP has not previously been well characterized. Although no mechanistic explanation for gastrointestinal wall changes in AP has been determined, it is reasonable that the anatomic proximity of the pancreas to the pylorus, duodenum, transverse colon, and jejunum could result in extension of local inflammation to these structures.
Our aims were (i) to report the prevalence and nature of ultrasonographic gastrointestinal wall changes in a referral population of dogs with AP, and (ii) explore associations between the presence of gastrointestinal wall changes and observed clinical and clinicopathologic variables. We hypothesized that the presence of neutrophilia, left shift, or toxic neutrophils, as surrogate markers of increased severity of inflammation, would be significantly associated with the presence of ultrasonographic gastrointestinal wall changes.

| Data collection and case selection
Ours was a retrospective cross-sectional study. The Small Animal Internal Medicine service case database at Langford Vets, University of Bristol, was searched from February 2012 to August 2020 using the search terms "pancreatitis, pancr*, AP, and ANP" (acute necrotizing pancreatitis) to identify dogs with a diagnosis of AP. For inclusion in the study, cases were required to meet all of the following inclusion criteria: • A full clinical history available for review, provided by the referring veterinary surgeon.
• Clinical signs compatible with a diagnosis of AP to include at least 2 of: vomiting, diarrhea, abdominal pain, lethargy, hyporexia, or jaundice.
• Abnormal canine pancreatic lipase assay (Spec cPLI, Idexx Laboratories, Wetherby, United Kingdom) or a cholestatic pattern on serum biochemistry as indicated by a disproportionate increase in serum alkaline phosphatase (ALP) or gamma glutamyl transferase (GGT) activities with respect to alanine aminotransferase (ALT) activity.
• At least 1 ultrasonographic abnormality compatible with a diagnosis of AP from the following criteria: pancreatic enlargement, parenchymal heterogenicity, parenchymal hypoechogenicity, hyperechogenicity of the peripancreatic mesentery or peripancreatic free fluid accumulation.
• An abdominal ultrasound examination with ultrasound report and still or real-time images available for review.
Cases were excluded based upon the following criteria: • Evidence of preexisting gastrointestinal disease in the dog's history characterized by ≥2 episodes of vomiting or diarrhea in the 2 months before presentation, excluding clinical signs considered related to the current problem.
• A laparotomy performed in the 2 weeks before referral.
• Administration of corticosteroids or nonsteroidal anti-inflammatory drugs (NSAIDs) in the month before presentation.
• Suspicion of pancreatic neoplasia clinically or ultrasonographically.
• Any concurrent disease process that might have altered ultrasonographic gastrointestinal wall appearance.
For evaluation of associations between clinicopathological variables and the presence of gastrointestinal wall changes, cases were further excluded if hematological data was lacking or if diagnostic evaluations identified any concurrent disease, other than AP, that might have resulted in a proinflammatory state or affect other clinicopathologic variables.

| Patient characteristics
Patient signalment, body weight, body condition score, clinical signs, and physical examination findings were extracted from the medical records. Patient comorbidities were recorded where present.

| Ultrasonographic examinations
All ultrasonographic examinations were either performed or supervised by a board-certified radiologist using an Acuson S2000 ultrasound system (Siemens GmBH, Erlangen, Germany) before 2019 or an Acuson S3000 ultrasound system (Siemens GmBH, Erlangen, Germany) from 2019 onward. All ultrasonographic images were retrospectively reviewed by a board-certified radiologist (E.R.) to confirm ultrasonographic evidence of AP and to evaluate for the presence or absence of gastrointestinal wall changes. Changes were then further characterized according to the following criteria: • Wall layering: reported as either normal or abnormal and specific abnormalities characterized as either an ill-defined appearance affecting specific layers, an ill-defined appearance affecting all layers or complete loss of wall layering.
• Wall thickening: reported as either normal or abnormal and specific abnormalities characterized as either generalized thickening or thickening with respect to a specific layer or layers. Reference values for normal gastrointestinal wall thickness were based on published data. 18 • Intestinal corrugation, reported as absent or present, with anatomic location(s). Reported serum biochemical data included ALT, ALP, and GGT activities and total bilirubin concentration. The cPLI assays were performed by IDEXX Laboratories (Wetherby, United Kingdom).

| Statistical analysis
Descriptive statistics (median, range) were used to present patient characteristics, clinicopathologic findings, and ultrasonographic findings. Ninetyfive percent confidence intervals (CI) were calculated for percentages using the latest available reported total UK dog population of 8.9 million. 19 A binary logistic regression model was used to assess for associa-

| Patient characteristics
From the initial search of the case database, 116 dogs were identified as having a diagnosis of AP recorded. Figure 1 demonstrates how 50 dogs were subsequently excluded through failure to meet inclusion criteria (n = 19) or fulfilling exclusion criteria (n = 31). Sixty-six dogs were included in part (i) of the study. Six dogs subsequently were excluded from part (ii) of the study, either because they lacked hematological data (n = 1) or because their comorbidities were considered likely to confound interpretation of clinicopathologic variables (n = 5).
Sixty dogs therefore were included in part (ii) of the study.

| Gastrointestinal wall changes
(n = 1) had wall thickening and corrugation concurrently. No dogs with colonic wall changes had a second concurrent change affecting the colon.

| Patient comorbidities
Of the 66 dogs included in parts (i) and (ii) of the study, 37.9% (n = 25) had a concurrent comorbidity. Diabetes mellitus was the most common comorbidity and was identified in 10.6% of the study population (n = 7), followed by diabetic ketoacidosis (DKA) in 9.1% (n = 6) and immune-mediated hemolytic anemia (IMHA) in 3% (n = 2).

| Association between clinicopathological variables and the presence of gastrointestinal wall changes
In the univariable logistic regression model, as presented in Table 3, both the presence of neutrophil toxic change and heart rate were significantly associated with the presence of ultrasonographic gastrointestinal wall changes. However, when carried forward to the multivariable model, only heart rate remained an independent predictor of the presence of ultrasonographic gastrointestinal wall changes (Table 4).

| DISCUSSION
We report in detail the prevalence and characteristics of gastrointestinal wall changes in a population of dogs with AP. In terms of patient Whereas 3.3% of dogs in that study had leukopenia, none had neutropenia. Similar serum biochemical abnormalities to those identified in our study also have been reported elsewhere, and generally reflect a cholestatic process characterized by increases in ALP and GGT activity disproportionate to ALT activity, sometimes accompanied by hyperbilirubinemia. Increased ALT activity also has been frequently reported, likely as a result of reactive hepatopathy secondary to the cholestatic and local inflammatory process. 12,13,[25][26][27] All of the dogs in our study had ultrasonographic evidence of AP according to the aforementioned criteria, combined with supportive clinicopathological features. Although a cholestatic pattern on serum biochemistry typically has not been necessary for inclusion in previous studies investigating AP, it remains a valuable means by which to increase clinical suspicion for pancreatic pathology, including pancreatitis, and therefore was utilized here. One dog was excluded based upon the presence of a pancreatic mass lesion detected ultrasonographically. It is well recognized that pancreatic mass lesions may be observed ultrasonographically in dogs with AP and in addition to reflecting focal AP, these might alternatively represent pancreatic neoplasia, abscesses, cysts or pseudocysts, although the latter 3 findings, typically would have a fluid filled aspect. 3,[10][11][12]28 Distinguishing between these requires pancreatic histopathology or cytology from fine needle aspirates, neither of which were performed in any of the dogs included in our study.
In our population, 47% of dogs with AP had concurrent gastrointestinal wall changes. Gastrointestinal wall changes were more commonly focal than diffuse, and the duodenum was the most commonly affected region of the gastrointestinal tract for all types of gastrointestinal wall abnormality (abnormal wall layering, abnormal wall thickness, and corrugation), which, given its anatomic proximity to the pancreas, is not surprising. Overall, wall thickening was the most common type of abnormality identified compared with abnormal wall layering or corrugation, and some dogs had ≥1 type of abnormality affecting the same region of the gastrointestinal tract.
Despite limited available literature on this topic, a study evaluating suspected gastric wall edema in dogs with AP noted that 2 of 14 dogs (14.3%) had complete loss of gastric wall layering. 14 Similarly, our study identified 1 dog with focal complete loss of gastric wall layering, which although often associated with neoplastic disease or ulceration, might be identified in AP secondary to local inflammation or potentially edema. The aforementioned study also reported the submucosa to be the most commonly abnormal individual gastric wall layer, which is in agreement with our findings, where 44.4% of dogs with abnormal gastric wall layering had submucosal involvement. 14 Another study reported duodenal changes in 18/46 (39.1%) dogs with AP and associated common bile duct obstruction, but did not report the nature of these changes nor the presence of other changes affecting the gastrointestinal tract. 28 Yet another study reported corrugation and thickening of the duodenal wall alongside gastric wall thickening in 12/38 (31.6%) dogs with AP, but some of those dogs were known to have a previous diagnosis of chronic enteropathy which potentially confounds these results. 15 Although the latter 2 of these studies did not characterize gastrointestinal wall changes in detail, all of the abnormalities reported also were identified in our population of dogs, which suggests they might be relatively common in dogs with AP.
Only heart rate was an independent predictor of gastrointestinal images. This approach might be considered a limitation because of the partly subjective nature of image interpretation, but the original reports were generated by several board-certified radiologists and radiology residents under their supervision, which helps to address this limitation to some extent. As discussed, abdominal ultrasonography has variable sensitivity for the diagnosis of AP. Therefore, it is possible that cases where the pancreas appeared normal might have been wrongly categorized as not having AP, and therefore not included in our study. Similarly, the left limb of the pancreas often is difficult to visualize on ultrasonographic examination and therefore cases with disease restricted to the left limb might have been missed and therefore also not included in our study.
Additionally, some dogs included in our study had normal serum cPLI (2 of 24 [8.3%] dogs in which cPLI was measured) and were included based upon ultrasonographic findings consistent with pancreatitis, in addition to a cholestatic pattern on serum biochemistry. However, it is recognized that the sensitivity of cPLI is between 70% and 81%, and therefore false-negative results are possible. 32 Histopathology was also not available for any of the cases in our study, which ultimately would be required to definitively diagnose AP and to exclude neoplasia as a cause of ultrasonographic pancreatic abnormalities. Additional follow-up, such as survival information and repeat ultrasonography to demonstrate resolution of gastrointestinal lesions, also would have aided in making this distinction.
In conclusion, ultrasonographic gastrointestinal wall changes were relatively common in this population of dogs with AP and were observed in approximately half of cases. Heart rate was the only clinical or clinicopathological variable independently associated with the presence of gastrointestinal wall changes. However, because of various possible contributing etiologies of tachycardia in this subset of dogs with AP, this finding is considered unlikely to be clinically useful in indicating whether GI wall changes are likely to be present. Our results however may aid clinicians in interpreting ultrasonographic gastrointestinal wall abnormalities in dogs with AP. They highlight that such abnormalities are relatively common, so therefore might be expected, and that even marked changes such as complete loss of GI wall layering might occur in conjunction with AP. However, a repeat ultrasound examination in such cases is recommended to document resolution of GI wall changes and to help exclude other causes of loss of GI wall layering (eg, neoplasia). Our results also provide a basis for further research into the clinical relevance of ultrasonographic GI wall lesions in dogs with AP and the mechanisms by which they occur. In particular, it would be useful to evaluate for a relationship between GI wall changes and increases in inflammatory markers such as CRP. Further work also is needed to evaluate for an association between ultrasonographic GI wall changes, disease severity, and outcome in dogs with AP and to establish whether these changes might have prognostic relevance.

ACKNOWLEDGMENT
No funding was received for this study.